Circuit closing device, especially for tests of switches



H. FORWALD Nov. 26, 1957 CIRCUIT CLOSING DEVICE, ESPECIALLY FOR TESTS OF SWITCHES Filed Dec. 12, 1955 INVENTOR. Haakon Tom/a Zd United States Patent F CIRCUIT CLOSING DEVICE, ESPECIALLY FOR TESTS OF SWITCHES Haakon Forwald, Ludvika, Sweden, assignor to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application December 12, 1955, Serial No. 552,600

Claims priority, application Sweden December 20, 1954 2 Claims. (Cl. 20081.5)

In short-circuiting tests with electrical switches. and other similar tests it is of great importance that the test circuit is closed with great accuracy at the intended closing moment. This is especially applicable with tests of polyphase switches, where it usually is necessary that the circuits of the diiferent phases are closed absolutely simultaneously with a deviation of at most a few electrical degrees. In certain cases it can even be necessary for carrying out a certain test that the circuits of the diiierent. phases are closed at different time periods. But then therelation between the closing periods can be determined in advance with great accuracy. In hitherto used arrange-- ments for carrying out short-circuiting tests, switches havebeen used which were released by some mechanical ar-- rangement, e. g. blocking hooks or the like, and the con-- tacts usually were arranged in the open air. But there were also used switches having their contacts arranged. in oil or in a compartment filled with compressed air, in order to decrease by this arrangement the length of theclosing arc. The present invention relates especially to closing switches having their contacts arranged in a com-- partment filled with compressed air, and the invention is: mainly characterized by the arrangement wherein the motion of the movable contacts of the switch is performed. by a piston operated by compressed air and movable in a. cylinder, which immediately before the closing of the switch is filled with compressed air, the piston, however, being held by a holding magnet, so that it cannot per form the closing of the switch before demagnetisation of' the holding magnet. Due to the fact that by this arrange-- ment the operating piston already from the beginning of" the release is influenced by the complete air pressure, a. practically constant acceleration of the contact bridge of the switch is attained and thus a great precision with regard to the closing moment.

The invention will be best understood with reference to the accompanying drawing in which Fig. 1 is a longitudinal sectional view of the circuit breaker, Fig. 2 is a side elevation of the holding magnet with the armature shown. in cross-section and Fig. 3 is a sectional view of the hold-- ing magnet. In the figures, 1 designates a compressed air" container, which by an intermediary Wall 2 is divided into two compartments 3 and 4 filled with compressed air' which is supplied by the pipe lines 5 and 6. A cylinder- 7 is attached to the intermediary wall, in which cylinder" there are arranged two pistons 8 and 9 joined togther by means of a piston rod 10 carrying a contact bridge 11,. which in the closed position of the switch is engaging thestationary contacts 12 and 13. These contacts are carried by leading through insulators 14 and 15 inserted in. the wall of the container 1. The container 1 is at the top provided with an inspection opening closed by a cover 16 and at the bottom with another opening closed by thecover 17, in which there is arranged a holding magnet 18. The cylinder 7 is by the intermediary wall 2 divided intov two compartments 19 and 20. The compartment 19 is through a pipe line 21 in communication with an elec Patented Nov. 26, 1957 ice trornagnetieally operated valve 22 and over this in communication with the compartment 4 through a pipe line 23. The valve 22 is operated by the current through the operating winding 24. An armature 25 is attached to the piston 9, which armature in the open position of the switch is held by the holding magnet 18. Further there is a spiral spring 26 arranged in the cylinder space 19, which spring has for its purpose to move back the pistons 8 and 9 to their lower position, when the compartment 19 is evacuated over the valve 22. The disk-shaped armature 25 is slightly excavated at its lower side, and the space 27 thus formed between the armature and the holding magnet is in communication with the open air by means of a channel 28 through the holding magnet. Thus the armature 25 is forced against the magnet 18 not only by the magnetic attraction but also by the air pressure in the compantment 4. Instead of a complete excavating of the armature 2-5, as shown in Fig. 1, the excavation can be replaced by a peripherical groove, as shown in Fig. 2.

As illustrated in Fig. 3, the holding magnet may suitably consist of a ring 29 of permanent magnetic material, which is attached at a yoke 30 of soft iron, from which a central core 31 of soft iron projects, which at the top 1s surrounded by a U-shaped pole ring 32 attached to the magnetic ring 29. Inside of this there is situated a demagnetisation winding 33. In order to decrease the size of the holding magnet and thus :to give it a higher speed, there may be also arranged one or a plurality of permanent magnets without any demagnetisation arrangement, and which are able to hold the piston 9 not by themselves but only in cooperation with the demagnetisable holding magnet.

In order to limit the motion of the pistons 8 and 9 and thus also the motion of the contact bridge 11, the piston rod 10 on top of the cylinder 7 is provided with a cross-rod 35, the ends of which move in two hair-pin shaped hooks 36.

The arrangement acts in the following way:

In performing a short-circuiting test there is obtained over the controller roll used at the test of switches a current through the winding 24, which current influences the valve 22 in such a way that the compartment 19 in the cylinder 7 is brought into communication with the open air over the pipe line 21. Immediately afterwards the holding magnet 18, also over the operating control, reaceives a release impulse through the Winding 33, and 'then the armature 25 is released so that the piston 9 by the pressure acting in the compartment 4 is moved upwards with a strong pressure until its movement is retarded by the air cushion formed in the upper part of the space 20 above the piston 8. The movement upwards is finally limited when the cross-rod 35 reaches the ends of the hair-pin shaped hooks 36. The contact bridge 11 then has forced itself between the stationary contacts 12 and 13. When then the circuit closing device shall be opened, the valve 22 formed as a three-path valve is reversed in such a way that the compartment 19, over the pipe lines 21 and 23, is brought into communication with the compartment 4, and as the pressure thus becomes the same on both sides of the piston 9, this is again moved downwards under the influence of the spring 26, until the armature 25 again is forced against the holding magnet 18.

I claim as my invention:

1. A current closing device for short-circuiting and similar tests with switches, comprising stationary and movable contact means, a compressed air source, a cylinder with one end permanently communicating with said compressed air source, a piston operating in the cylinder and connected to the movable contact means, said piston being permanently exposed to the air pressure in the compressed air source so that such air pressure exerts an opand serving to hold the movable contact means in the open position of the contacts against theforceofthe 5 compressed air acting on the piston until the magnet is given a releasing impulse.

2. A current closing device according to claiin ;1, comprising a compartment filled with compressedv iry-and in which the holding magnet is arranged in said-compartment, and in the open position of the movable contact means the magnet and the armature form a confined space which communicates through a channel with the open References Cited in the file of this patent UNITED STATES PATENTS 692,217 Sundh Jan. 28, 1902 1,737,649 Edsall Dec. 3, 1929 2,302,685 Dyer Nov. 24, 1942 2,449,518 Strom Sept. 14, 1948 2,479,315 Coggleshall Aug. 16, 1949 2,671,317 Heintzelman Mar. 9, 1954 2,740,859 Beatty et a1. Apr. 3, 1956 

